Preheat the oven to 350°F (175°C). Grease a loaf pan.

In a mixing bowl, mash the ripe bananas until smooth.

Stir in the melted butter, beaten egg, and vanilla extract until well combined.

In another bowl, whisk together the flour, cocoa powder, baking soda, salt, and sugar.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Fold in chocolate chips if using.

Pour the batter into the prepared loaf pan.

Bake in the preheated oven for 60 minutes, or until a toothpick inserted into the center comes out clean.

Allow to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.